Centre for Green Technology, School of Civil and Environmental Engineering, University of Technology Sydney, NSW 2007, Australia.
Environmental Protection Department, Hong Kong Special Administrative Region Government, Hong Kong.
Sci Total Environ. 2022 Dec 1;850:158004. doi: 10.1016/j.scitotenv.2022.158004. Epub 2022 Aug 12.
High-mileage vehicles such as taxis make disproportionately large contributions to urban air pollution due to their accelerated engine deterioration rates and high operation intensities despite their small proportions of the total fleet. Controlling emissions from these high-mileage fleets is thus important for improving urban air quality. This study evaluates the effectiveness of a pilot repair program in reducing emissions from taxis in Hong Kong which account for about 2 % of the total licensed vehicles. The emission factors of a large sample of 684 in-service taxis (including 121 for an emission survey program and 563 for a pilot repair program) were measured on transient chassis dynamometers. The results showed that 63 % of the sampled taxis failed the driving cycle test before the pilot repair program. Most of failed taxis were NO related and 91 % of failed taxis exceeded the emission limits of at least two regulated pollutants simultaneously. After the pilot repair program by replacing catalytic converters and oxygen sensors, the failure rate was significantly reduced to only 7 %. In addition, the fleet average NO, HC and CO emission factors were reduced by 85 %, 82 % and 56 %, respectively. In addition, on-road remote sensing measurements confirmed the real-world emission reductions from the taxis that participated in the pilot repair program. These findings led to the implementation of a large-scale replacement program for all taxis in Hong Kong during 2013-2014, which was estimated to have reduced the total HC, CO and NO emissions by about 420, 2570 and 1000 t per year, respectively (equivalent to 5-8 % emission reductions from the whole road transport sector). Therefore, reducing emissions from the small high-mileage fleets is a highly cost-effective measure to improve urban air quality.
高里程车辆（如出租车）由于发动机老化速度加快和高运行强度，尽管其在总车队中的比例较小，但对城市空气污染的贡献不成比例。因此，控制这些高里程车队的排放对于改善城市空气质量非常重要。本研究评估了香港出租车试点维修计划对减少排放的有效性，香港的出租车约占总许可车辆的 2%。在瞬态底盘测功机上测量了一个由 684 辆在役出租车组成的大样本的排放因子（包括 121 辆用于排放调查计划和 563 辆用于试点维修计划）。结果表明，在试点维修计划之前，有 63%的抽样出租车未能通过驾驶循环测试。大多数失败的出租车与 NO 有关，91%的失败出租车同时超过了至少两种受监管污染物的排放限值。在试点维修计划中通过更换催化转化器和氧传感器后，故障率显著降低至仅 7%。此外，车队平均 NO、HC 和 CO 排放因子分别降低了 85%、82%和 56%。此外，道路遥测测量结果证实了参与试点维修计划的出租车在实际行驶中的减排效果。这些发现促使香港在 2013-2014 年期间为所有出租车实施了大规模的更换计划，据估计每年可减少总 HC、CO 和 NO 排放量约 420、2570 和 1000 吨（相当于整个道路交通部门减少 5-8%的排放量）。因此，减少小而高里程车队的排放是改善城市空气质量的一种非常具有成本效益的措施。
